Loss of finger or hand function severely affects an individual's ability to perform manual tasks. Prior orthotic devices have restored limited hand function to individuals unable to control finger movement. These devices use robotic technologies and actuate fingers through use of motors or other mechanisms.
There are myoelectric devices for the purpose of enhancing or restoring functional use of the hands of those who have a disability of the upper extremity distal to the elbow. Prior art myoelectric devices are large, bulky devices. They also often require large and heavy batteries due to the amounts of electrical current and/or voltage needed to power them.
Other orthotic devices have used shape memory alloy wires made of Nitinol or like materials as actuating members. The Nitinol wire forms part of an electrical circuit that selectively flows current through the Nitinol wire to heat the wire to a transition temperature that contracts the wire. The wire contraction actuates a member joined to an orthotic to move an otherwise uncontrollable finger.
US 2006/094989 discloses a movement facilitation device for the movement of a joint or limb. It uses shape memory alloy wires in one embodiment that contract to provide movement to a joint. This device is for therapeutic rehabilitation and does not offer active control over strength or range of motion.
The use of shape memory alloy wire's contraction to actuate orthotic devices is problematic. A long Nitinol wire is usually required to generate a sufficient contraction stroke for finger actuation. Heated Nitinol wire only shrinks about 3% of its unheated length. The long wire length necessitates prior orthotic devices to include large support portions to accommodate the coils of long shape memory alloy wires.
Another problem with prior orthotic devices that use SMA is with heat. Some rely on radiation to cool the coils of long, hot, contracted wire below the transition temperature and return the wire to its original length prior to another contraction. Radiation cooling slows wire relaxation/lengthening and causes a time delay before the joint can be moved again.
US Patent Application 2012/0022666 discloses a system for moving a prosthetic finger. The device could be a glove worn over a damaged finger. It uses shape memory alloy wire to articulate the finger. The device includes a cooling system for each wire. It uses the contraction of the length of wire when heated above transition temperature to create tension on another wire running along the top of the finger. This then pulls more wires to create movement of the finger at each joint. This is a bulky and complex system of heating and cooling shape memory alloy wires.
Accordingly, there is a need for an orthotic device that is portable and that will comfortably, safely, and intuitively restore the functional use of the hand or hands of those who are disabled. The preferred device would be myoelectric, lightweight, slim, and energy efficient—requiring relatively few small batteries and making it safe and comfortable to wear all day. There is a further need for an orthotic device that provides individual, articulate control over each joint of each finger, which allows for control over the range of motion and force by which each joint is moved.